This invention pertains to digital sound generation systems and particularly to systems which simulate the three dimensional position of one or more sound emitters and/or reflective surfaces relative to a sound receiver.
Extensive research has been done to model the way human listeners determine the location and velocity of one or more sound emitters. In short, it has been determined that the brain relies on numerous so-called "cues" or properties of the received sound that indicate the location and/or velocity of an emitter. Perhaps the simplest cue is the loudness of the sound; a loud sound will seem closer than a faint sound.
Another cue is the arrival time of a sound at each ear. For sounds originating from locations off to the left or right side of the listener's head there is a relatively large difference between arrival times at each ear, the so-called inter-aural time delay or ITD. For sounds originating in front of or behind the listener the ITD value is relatively small. A large body of literature describes numerous such cues and their interpretation in detail.
Human listeners are further sensitive to the location of reflectors. Sound from a given emitter may arrive via one or more paths including a path that includes a reflection from a surface. The resulting distribution of arrival delays is a cue to the acoustic environment.
Cues indicating location, motion, and reflective environment may be synthesized to enhance the realism of sound reproduction. Cue synthesis finds application in cinema sound systems, video games, "virtual reality" systems, and multimedia enhancements to personal computers. The existing cue synthesis systems exhibit shortcomings. Some do not generate accurate cues and thus do not effectively simulate an emitter's position. Others introduce unwanted audible artifacts into the sounds to be reproduced.